The proposed research program is concerned with the role of temporally varying signals in determining the sensitivity of the visual system. Specifically, the existence of mechanisms selectively sensitive to the spatial and the temporal aspects of the stimulus will be explored. Temporally varying signals under consideration include the neural activity induced by the onset and the offset of the stimulus itself, as well as the activity produced by image motion occuring during fixation. There are three major divisions: 1) Human psychophysics, 2) Human electrophysiology, 3) Animal electrophysiology. For studies under 1 and 2 the basic method is that of image stabilization. In this way, temporal stimulation normally provided by image motion is eliminated. In the first series of experiments, sensitivity measured under these stable conditions is then compared to measures obtained under conditions wherein temporal luminance variations are imposed experimentally, or permitted to occur as a result of normal eye movements. Sensitivity will be indexed by the thresholds for detecting spatial contrast and by the thresholds obtained during dark adaptation after stabilized and unstabilized bleaches. In the second series of experiments, an attempt will be made to correlate the changes in the appearance of a stabilized image with visual cortical potentials evoked (VECP) by the onset of the image and by the micromovements of the eye. The third series of experiments will utilize acute animal preparations and will be designed to supplement human psychophysics in search of independent neural channels specialized or processing the spatial and temporal aspects of visual information.